Sorta but not quite. They do share a lot of parts- like the GM Sniper Custom, GM Guard Custom, have the same torso and skirt armor, but different head/legs. The GM Interceptor has the same torso as the GM Sniper Custom but has the lower body of the GM Cannon Space type. GM Cannon Space type has a unique torso and shares its lower body with the Interceptor.

Basically between the four kits, they share two torso types, one lower body type (and two completely unique), the same arms (with the Guard Custom and Sniper Custom having box beam sabers,) two different sets of skirt armor, and unique heads. But I'm unsure about the backpacks as we've only seen the rear view of the GM Sniper Custom and GM Guard Custom.

The GM Cannon SHOULD have a unique backpack (but then again, most of the GM Guard Custom should have been different from the GM Sniper Custom...) so I can't tell at this point.